“Cutting down on salt doesn’t reduce your chance of dying,” broadcasts the press release for a meta-analysis of trials relating salt intake to cardiovascular disease, published today in the American Journal of Hypertension. But don’t reach for the pretzels and potato chips just yet. This sentiment does not reflect the results of the analysis, says the study’s lead author Rod Taylor, a health services researcher at the University of Exeter University in the UK. “We are explicitly not saying that,” he told Nature Medicine.

Whether curbing salt intake is necessary is still up for debate. The US Institute of Medicine recommends ingesting only 2.3 grams of sodium daily, citing studies linking salt to high blood pressure and heart failure. But some critics argue that the clinical evidence for this upper limit is scarce. For example, in a correspondence to Nature Medicine last year (written in response to our news feature ‘Parse the salt, please’), Morton Satin, vice president of the Virginia-based Salt Institute, called for better clinical trials before seeking a “solution to what may be a nonexistent problem.”

The new meta-analysis compiled data from seven randomized clinical trials, pooling more than 6,000 study subjects, to determine whether reducing dietary salt intake has any effect on mortality and cardiovascular disease. Notably, six of the seven trials did not directly manage the diets of the participants. Rather, people in those trials received advice to help them reduce their salt intake, an intervention that measures subject behavior more than the biological effects of salt.

The authors of the meta-analysis did not aim to review studies that examined behavior in such a way, but those are the only non-biased trials that have been performed, says Taylor. “Reviews and evidence up to now have been based on these non-experimental studies” that accept volunteers who want to reduce their sodium, he says. Those who volunteer are more likely to engage in other healthy behaviors, making it difficult to judge the effects of salt reduction alone, Taylor notes.

Unlike the journal’s press release, the meta-analysis indeed found “moderate evidence” that those who were advised to reduce their salt intake had lower blood pressure and less sodium in their urine 2–3 years after starting the low-salt diet. But ten years later, these participants had returned to their former state. If anything, the analysis shows that it’s “very hard to maintain behavioral adaptations,” says Taylor. “It’s not surprising therefore that there was no survival benefit.”

Thus, the take-home message, it seems, is not that salt is okay for you, but just that cutting down on salt is easier said than done.

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